Electrical measuring instrument



Dec.-1s, 1934. n. T. FAus 1,985,082

ELECTRICAL MEASURING INSTRUMENT Filed oct. 5, 1933 Patented Dec. 18, 19.34 I I y y u UNITE-D STATES PATENT OFFICE ELECTRICAL MEASURING INSTRUMENT Harold 'I'. Fans, Lynn, Mass., assignor to General glecric Company, a corporation of New Application October 5, 1933, `Serial No. 692,272

v11 Claims. (Cl. 171-95) My invention relates to electrical instruments the axis of rotation ofthe element 11. The anand concerns particularly magnetic eld arnular returnelement 21 serves also as a magnetic rangements for use with electrical instruments shield, protecting the instrument from the effect of the D'Arsonval type. of terrestrial'magnetism or stray fields produced It isan object of my invention to provide magby other electrical or magnetic apparatus. 5

netic field constructions which will permit read- The lateral surfaces 22 of the permanent magily producing at relatively low cost, compact, nets 19 and 20 are radial planes passing through sensitive electrical instruments having substanthe axis 16-16 of the annular segments 19 and tially uniform scale distribution. Other and fur- 20, and the annulus 21. The'per'manent magnets l0 ther objects of my invention will become apparent 19` and 20 are magnetized in such a manner that l0 as the description proceeds. t t the magnetic lines of force and the flux therein In carrying out my invention in its preferred pass radially through said magnets, as indicated form, I employpermanent magnets having conby the arrows-in Fig. 7, making the magnets 19 cave cylindrical pole faces opposite each other and 20 the equivalent of a large number of bar with a core for a moving coil placed between said magnets of equal length. Consequently, the pole l5 pole faces to form air gaps for said movable coil, strength of the magnets is substantially uniform and I utilize an annular magnetic return unit across their pole faces 24 and 25. Likewise the surrounding said permanent magnets and in conflux density in the air gap 23 of the instrument tact with their oppositely extending pole faces. is substantially uniform throughout the air gap, The features of my invention, which I believe resulting in a uniform scale distribution. The 2,0 to be novel and patentable, will be pointed out use of permanent magnets in the shape of segin the claims appended hereto. A better underments of an annulus permits a compact instrustanding of my invention, itself, may be obtained ment construction, and also permits obtaining a by referring to the following description taken relatively uniform flux in the air gap notwith- 25 in connection with the accompanying drawing in standing the fact that the length 4of the pole faces V25 which Fig. 1 represents a plan view of one emis relatively great in comparison with the lengths bodiment of my invention; Fig. 2 is a vertical of the magnets. AIn the embodiments, where this section of the embodiment illustrated in Fig. 1; relationship between the length of pole face and and Fig. 3 is an exploded view in perspective of the length of magnet exists, it is desirable that the instrument mechanism of the embodiment the lateral surfaces 22 should be substantially 30 shown in Figs. 1 and 2. Fig. 4 illustrates in plan -radial in order that the length of the magnets' a second embodiment of my inventionpFig. 5 is in the direction of magnetization will be substana vertical section of the embodiment of Fig.v 4; tially equal throughout and the same magnetic Fig. 6 is an exploded view in perspective of the strength will'be obtained across the pole face.

instrument mechanism .of the embodiment of The magnets 19 and 20 are preferably com- 35 Figs. 4 and 5; and Fig. 7 is a schematic diagram posed of magnetic material having a relatively illustrating the manner in which the permanent high coercive force such as, for example, cobalt magnets utilized in the instruments constructed steel or an aluminum-nickel alloy of iron comin accordance with my invention may be magposed of approximately 6 to 15% aluminum and 40 netized. Y approximately 20 to-30% nickel. A convenient 40 Referring now more in detail to the' drawing -Way of magnetizing the permanent magnets is to in which like reference characters refer to like 'assemble the instrument mechanism completely parts throughout, in the arrangement of Fig. 1, and to'place it between poles 26 of any suitable the instrument comprises an instrument mech.- magnetizingarrangement, preferably an electroanism consisting of a movable element 11 and mgnet- Thepeles 26 have COIlCeVe Cylindrical 45 a magnetic acid una 12 mounted on a sammler pole races 2v fitting the outer Surface 0f the anbase 13 in a casing, not shown, and provided with nulus 21 and, since the poles 26 and the annulus a scale 14. 'Ihe movable element consists of a 21 are Composed 0f relatively high permeebility current conducting coil 15 suitably mounted to magnetic material, the magnet lines 0f 'Olee '0 permit `rotation about an axis ic-is' and a. tend to pass along normls to the pole faces 27 5 pointer 1"! cooperating with lthe scale 14. The or radially through the permanent magnets 19` magnetic eld comprises a cylindrical coreI 18, a and l20, as indicated by the arrows. Such a high pair of permanent magnets 19 `and 20 having the magneto-motive 'force is used in magnetizing the shape of segments of an annulus and an annular instrument that the, annulus 211 becomes satumagnetic return 21, all substantially coaxial with rated and a magnetizing flux is forced across the 55 airgaps.23 and through the permanent magnets 19 and 20 in a radial direction.

When instruments of specially high sensitivity are required, it may be desirable to increase the length of the permanent magnets as shown in the embodiment of Fig. 4. In this embodiment, the annular magnetic return element 21 is increased to substantially the diameter of the casing of the instrument and bar magnets 28 and 29 are employed. The magnets 28 and 29 are Ahave their lateral surfaces 22 along substantially radial planes in order that the magnetic lines of force in the portion of the magnets near the air gaps will be substantially normal to the pole faces, the pole strength will be substantially uniform along the pole faces, and a substantially uniform flux strength will be produced in the air gap. It will be understood that, in magnets of greater length relative to .the length of pole faces as shown in the embodiment of Fig. 4, less diillculty is experienced in obtaining uniform flux strength in the air gap. Forthis reason, it is not absolutely essential to extend the radial surface 22 to the inner surface of theannulus 21 as shown in the arrangement of Fig. 1, although, if desired, such a construction may also be employed yin connection with the embodiment of Fig. 4.

Although I lhave described and'illustrated the method of carrying out my invention in connection with indicating electrical instruments, it 'will be understood that v my inventionis not limited thereto but, obviously, includes applications in recording instruments, contact making instruments, etc.

In accordance with the provisions of the patent statutes, I have described the principle of 0perationof my invention together with the apparatus which I now consider to .represent the best embodiments thereof, and I desire it to be understood that the apparatus shown and described is only illustrative and that the invention may 'be carried out by other arrangements.

What I claim as new and desire to secure by Letters Patent of the United States is: e

1. An electrical instrument comprising in combination a rotatable currentconducting coil, a

cylindrical magnetic core substantially coaxial with the axis of rotation of said coil, a pair of .radially magnetized permanent magnets of relafield arrangement therefor comprising a ring of Y high permeability magnetic material, and a pair of permanent magnets of high coercive force material having the shape of segmentsy of an annulus with their outer surfaces in contact with the inner surface of said magnetic ring, said magnets being magnetized in aradial direction and being located opposite each other.

3. A magnetic field member for electrical instruments comprising a magnetic core bounded by a surface of revolution, apair of permanent magnets of high coercive force material having inner pole faces lying along a surface of revolu- `.tion substantially coaxial with said core and having outer pole faces, an air gap being formed between said core and said inner polefaces of said permanent magnets, said permanent magnets being magnetized in directions substantially along normals to their inner pole faces, and a magnetic return element in contact with the outer pole faces vof said permanent magnets.

4. A magnetic field member for an electrical instrument comprising a magnetic return element, a pair of permanent magnets of high coercive force material .having outer pole faces in contact with said magnetic return element and having inner pole faces opposite each other, and a cylindrical core located between said innen pole faces andv spaced therefrom to form a pair of Aair gaps, the inner ends of said permanent magnetis being lbounded by cylindrical surfaces substantially coaxial with the axis of said core to form said inner pol`e faces and planes at the edges of said inner polefaces substantially coinciding with planes including the axis of said core and outer pole faces, a magnetic core between said inner pole .faces and a magnetic return element joining said outer pole faces, said permanent magnets being relatively short in the direction of magnetization in comparison with the lengths of their pole faces, and being magnetized along normalsv to their inner pole faces.

6. In a magnetic field structure for an electrical instrument,' a permanent magnet having the shape of a segment of an annulus and magnetized along radii of tlie circles forming said annulus.

7. In a magnetic field structure for an electrical instrument, a permanent magnet having lateral surfaces generated by radial lines intersecting a common axis, and having at least one pole face lying along a surface of revolution coaxial with said axis, said magnet being magnetized in directions lying along normals to said pole face.

8. Ina magnetic eld structure for an electrical instrument, a permanent magnet having pole faces lying along concentric surfaces of rev olution and being magnetized along normals to the inner pole face.

9. In a magnetic field structure for an elec.

trical instrument, `a permanent-magnet having pole faces lying along a surface of revolution and being magnetized along normals to said pole faces,.the length of said magnet in the direction of magnetization being relatively short in `comparison with the length of said pole faces.

10. A magnetic field unit' for an electrical instrument comprising in combination a substanti'ally cylindrical magnetic core, a pair of permanent magnets having the shape of segments of an annulus, and an annular magnetic return element, the circular surfaces of said permanent magnets forming their pole faces, the outer-pole faces being in contact with the inner circular surface of said annular magnetic return element and the inner pole faces being spaced from said cylindrical core to formr air gaps, said permanent nngnets being radially magnetized.

11. A magnetic neld unit for an electrical in strument comprising an annular magnetic return unit, a pair of permanent magnets of unequal lengths placed with their magnetic axes in line,

having concave cylindrical pole faces facing toward each other and convex cylindrical pole faces facing away. 'from each other and a substantially cylindrical core placed between the said concave cylindrical pole faces and 'spaced therefrom to form a pair of air gaps, said convex cylindrical pole l faces and the inner surface -of said annular magnetic return element having equal radii and said convex pole faces being in contact'wlth the inner surface of said annular return element.

HARQID T. FAUB. 

